Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$49.25	4.304%	$51.3697	$51.37	$51.35	$51.40
Purchase #2	$166.66	10.480%	$184.126	$184.13	$184.15	$184.10
Purchase #3	$19.59	6.459%	$20.8553	$20.86	$20.85	$20.90
Purchase #4	$25.96	3.600%	$26.8946	$26.89	$26.90	$26.90
Purchase #5	$125.33	5.180%	$131.8221	$131.82	$131.80	$131.80
Purchase #6	$163.82	5.569%	$172.9431	$172.94	$172.95	$172.90
Purchase #7	$103.93	4.472%	$108.5777	$108.58	$108.60	$108.60
7 purchase totals =	$654.54		$696.5885	$696.59	$696.60	$696.60